Method of operating a vehicle transmission

ABSTRACT

Specific shift positions of an electrically actuated vehicle transmission, such as first to fifth, neutral and reverse gears, are detected by monitoring one or more characteristic electrical variables, e.g., actuator currents, during a shift movement of the transmission and by correlating increased or decreased levels of current with the arrival at or passage through the specific shift positions.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser.No. 10/012,701, filed Dec. 7, 2001, which is hereby incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

The invention relates to a method of detecting at least onepredetermined shift position of a vehicle transmission among a pluralityof different shift positions corresponding to different rotary transferratios between an input shaft and an output shaft. It further relates toa control device, to a vehicle transmission, as well as the use of themethod, the use of the control device, and the use of the vehicletransmission. In addition, the invention also relates to a method ofdetecting a position change in relation to a reference position of avehicle transmission.

A transmission in the present context means a device that can be shiftedinto different states, by an either stepwise or continuous variation, togenerate different rotary transfer ratios between two shafts. Thetransmission is configured as a gear-changing transmission or acone-pulley transmission, or other appropriate mechanism. The shiftprocesses of the transmission can be controlled automatically ormanually, or in a partially automatic mode, or in an automated mode thatpermits manual intervention by the driver. A transmission in the senseof the present invention can be configured so that shifts from one gearratio to another cause an interruption in vehicle traction, or it can beconfigured to perform shifts without interrupting traction.

With preference, the transmission is configured as an automatictransmission which, in the context of the present invention, means atransmission that shifts without interrupting traction. With specialpreference, however, the transmission is configured as an automatedshift transmission, a term which is used in particular for atransmission in which the control of the shift process is automated butcauses an interruption in vehicle traction.

Transmissions as well as operating methods for transmissions belong tothe known state of the art.

In a manual transmission, the gear shifts are performed manually by thedriver. In principle, the driver is free to shift arbitrarily from anygear into any other gear. The driver chooses when to shift gears andwhich gear to shift into, based on certain criteria. The driver willdecide to shift gears particularly in response to the sound of theengine and depending on which of the gears is currently engaged.

Errors in recognizing which gear is currently engaged, errors ofshifting into an other than the intended gear, judgment errors about theneed to shift gears, or other mistakes can cause damage to atransmission or can stall the engine of a vehicle. This kind ofsituation can occur, for example, in a vehicle coasting downhill withthe transmission set to the neutral position, if the driver's foot is onthe gas pedal so that the engine runs at a high rpm rate but the drivererroneously believes the transmission to be in first gear and thereforeshifts into second gear.

Also known are automated shift transmissions in which the shifts areactuated by two electric motors. The electric motors apply a force to ashifter finger. The shifter finger moves in a pattern that consists of aselector track (also called neutral track) and shift tracks branchingoff from the selector track. The first of the electric motors moves theshifter finger in the direction of the shift tracks which terminate atthe different gear positions, while the second of the electric motorsmoves the shifter finger in the direction of the selector track wherethe transmission is in the neutral state.

The shifter finger position is monitored by displacement sensors whichare arranged at the electric motors and work according to an incrementaldetection principle.

The shifter finger is controlled by the electric motors dependent on theposition values generated by the incremental sensors.

Automated shift transmissions of the foregoing description provide asatisfactory level of shifting and driving comfort and an economical wayof operating a vehicle.

However, there have been incidents where gear shifts where performedincorrectly by transmissions of this type. Incorrect gear shifts aredetrimental to the driving comfort in a vehicle with an automated shifttransmission and will shorten the life of the transmission.

OBJECT OF THE INVENTION

The present invention therefore has the objective of providing a methodof operating a vehicle transmission, as well as a transmission capableof performing the method, with an at least reduced incidence ofincorrect gear shifts, a longer operating life, and an improved level ofcomfort for the driver and passengers of a vehicle that is equipped withthe inventive transmission. In particular, the invention has theobjective of providing a method of operating a transmission, as well asa transmission capable of performing the method, wherein the currentshift position or shift movements from one position to another can bedetected and evaluated more accurately and reliably and whereindetection errors can be corrected, so that detected positions or shiftmovements reflect the actual positions or movements of the transmission.

SUMMARY OF THE INVENTION

To meet the objective stated above, the invention proposes a method ofdetecting at least one predetermined gear-shift position of atransmission that has a plurality of different operating statescorresponding to different rotary transfer ratios between an input shaftand an output shaft of a vehicle transmission. A transmission that isoperable by the inventive method has a shift pattern with a selectortrack and shift tracks. A first shifter element, in particular a shifterfinger, is movable within the shift pattern. The transmission alsoincludes a second shifter element, in particular a shifter shaft or ashift rod. The transmission is further equipped with an actuator devicerunning under the control of an electrical control device to actuate atleast one of the first and second shifter elements. At least oneposition-sensor device is provided in the transmission to determine theposition of a movable element of the transmission.

The method according to the invention has the following steps:

a) When a set of predetermined conditions are present, an actuatingforce is applied by the actuator device to at least one of the shifterelements in accordance with a predetermined characteristic.

b) At least one characteristic electrical variable of the actuatordevice and/or the control device, particularly an electric current, ismonitored as a function of time.

c) The profile of the electrical variable as a function of time isevaluated according to a predetermined evaluation characteristic todetermine a shift position that the transmission is set at. Thisdetermination is based on a functional dependency between the timeprofile of the characteristic electrical variable and the shiftposition.

The shift positions to be determined by the inventive method include inparticular at least one end position of a shift-track and/or at leastone specific position in the selector track and/or any position in theselector track.

The second shifter element, which consists of a shifter shaft, a shiftrod, a shift fork, or a similar element, is connected to the firstshifter element.

The arrangement of a selector track and shift tracks, as well as thefirst and second shifter elements, are part of a gear-shiftingmechanism.

At least one movable element of the gear-shifting mechanism, such as thefirst or second shifter element, can be subjected to actuating forcesunder the control of an actuator device, causing the element to move, atleast to the extent that the movement is not prevented by other factorsor elements of the mechanism, such as end stops.

An actuator device in the sense of the present invention is a devicethat can convert one form of energy into another, generating an outputthat actuates the shift mechanism or at least one of the movableelements of the shift mechanism. In particular, the actuator device hasat least one electric motor that converts electrical energy intomechanical motion. With preference, the actuator device has two electricmotors. The first motor, referred to as selector motor, can exert on thefirst shifter element a force in the direction of the selector track.The second motor, referred to as shifter motor, can exert on the firstshifter element a force in the direction of the shift tracks.

A shift track in the sense of the invention can mean a physicallyexisting shift track or a virtual shift track containing a position ofthe first shifter element where a predetermined gear or a predeterminedrotary transfer ratio of the transmission is engaged, or it can mean apair of shift tracks branching off from a given point of the selectortrack.

A virtual track means a concept where the shifter element can move onlyalong certain track-like paths, constrained by the nature of controlsignals generated by the actuator device or the control device.

The actuator device is controlled by a control device.

A control device in the sense of the invention means in particular adevice that supplies control signals and/or energy to the actuatordevice in accordance with a predetermined characteristic. In particularaccording to the inventive concept, the nature, duration, timing,direction, orientation, and force of the action exerted on the shiftmechanism by the actuator device depends on the signals and/or on theflow of energy transmitted from the control device to the actuatordevice.

The invention provides in particular that the control device suppliesthe actuator device with current, i.e., with electrical energy,according to a predetermined characteristic.

A control device in the sense of the invention can be designed toprovide energy and/or to control either the actuator device alone or atleast one other device in addition to the actuator device, for example aclutch. Under a preferred concept of the present invention, the controldevice controls the actuator device through one or more voltage signalswhich may be of a set magnitude or variable according to a predeterminedcharacteristic.

According to the invention, the transmission is equipped with a positionsensor device that serves to detect shift positions by sensing thepositions of components that are moved in the process of shifting.

A position sensor device in the present context means a device by whicha position or a change of position can be detected in absolute orrelative terms. In particular, the position sensor device can consist ofa device that measures the length of a linear displacement or the angleof a rotary displacement. In particular, the position sensor device isconfigured to perform either an absolute measurement or an incrementalmeasurement.

According to the invention, the actuator device will in the presence ofcertain conditions exert a force on at least one of the shifter elementsin accordance with a predetermined characteristic, while during theactuation at least one characteristic electrical variable of the controldevice and/or the actuator device is detected and/or monitored as afunction of time.

A characteristic electrical variable in the sense of the presentinvention is in particular a voltage or a current.

With preference, the characteristic electrical variable to detect ormonitor is the total amount of current consumed and/or generated by thecontrol device and/or the current consumed by the selector motor and/orthe current consumed by the shifter motor and/or the current consumed bythe actuating device. In particular, the process is voltage-controlled,where voltage signals are given according to a predeterminedcharacteristic, and the currents flowing as a result of the voltages aremonitored or detected.

Instead of monitoring a current, it is also possible within the scope ofthe invention to monitor another characteristic electrical variable. Torepresent the invention in simple terms, the example of a voltagecontrolled method is explained, in which a predetermined current ismonitored or detected. However, the invention also includes conceptswhere another first characteristic electrical variable is used insteadof a current, or another second characteristic electrical variable isused instead of a voltage.

According to the invention, the characteristic electrical variable,meaning the current in the case of the representative example, isevaluated as a function of time according to a predetermined evaluationcharacteristic in order to determine at least one of the shift positionsof the transmission.

The predetermined shift positions that can be detected by one of theembodiments of the inventive method are in particular one or more of theshift-track end positions and/or the neutral position and/or anyposition where the first shifter element is located in the selectortrack.

The invention provides in particular that the evaluation of the currentas a function of time will indicate when the first shifter element ispositioned at a dead end, detents, specific locations within a track, orit will indicate in which track the shifter element is currentlypositioned.

The invention will be explained in further detail through the example ofa transmission with a shifter finger, where the latter is representativeof any kind of first shifter element.

In the present context, if a first shifter element or shifter finger issaid to run against a stop, dead end, or boundary, the latter terms areunderstood to mean either an actual physical barrier or the occurrenceof an effect that is comparable to a physical barrier. An effectcomparable to an actual physical barrier means in particular thatanother element that is coupled to the movable element is running into astop or is otherwise constrained from continuing its movement. Aconstraint that prevents a continued movement can be realized inparticular by a preset limit in the control device or the actuatordevice. For example, an electric motor can be controlled so that it isswitched off when reaching a predetermined amount of displacement in agiven direction under a given set of conditions.

In the present context, if a movable element such as the first elementor shifter finger is said to have reached an indent in a surfaceprofile, or a detent, this means that the element is engaged in anactual physical detent or an analogous position-defining feature, orthat another element that is coupled to the first element has a detentfeature that is in an engaged position.

The invention has the advantage that predetermined positions of thetransmission can be safely recognized even in case of a failure of theposition sensor device, so that incorrect gear shifts are avoided. Forexample, the invention provides the possibility of detecting end stopsof the transmission, the release of a blocked synchronizer, a detentposition for the neutral state, or bias-free, settled positions of thetransmission. The invention further provides the possibility that theposition sensor device will adapt itself to these positions.

As a preferred concept, a method according to the invention can be usedas an emergency mode that is used under a predetermined set ofconditions. In particular, the emergency mode is started if the positionsensor device has been found to produce faulty information or if it hasfailed completely, or produces signals that are contradicted by otherfactors.

In accordance with a particularly preferred embodiment of the invention,the electric current that is being monitored depends on the activitiesof the selector motor and/or the shifter motor in accordance with apredetermined characteristic. In particular, the electric current isstronger at times when the selector- and/or shifter motor is running.When the selector- and/or shifter motor consumes an increasing amount ofpower, the monitored electric current will likewise show an increase.

The invention provides in particular, that starting and braking currentsare taken into account in the evaluation in accordance with apredetermined characteristic.

According to a particularly preferred embodiment of the invention, themonitored electric current depends in a predetermined characteristicmanner on the travel path of the shifter finger and/or on the force thatis exerted on the shifter finger by the actuator device.

Preferred is a concept where the electric current represents a combinedcharacteristic effect of the activities of the selector- and/or shiftermotor, the travel path of the shifter finger and/or the force acting onthe shifter finger.

In particular, the invention provides that variable amounts ofresistance opposing a movement of the shifter finger will have aninfluence on the electric current. In particular, by monitoring thecurrent as a function of time, it is possible to determine whether theshifter finger is being pushed against an end stop and/or is positionedat an end stop and/or is running through a detent position and/or islocated at a detent position and/or whether a movement of the shifterfinger in a shift track has arrived at the selector track, or otherinformation about the movement and/or position of the shifter finger. Asa particularly preferred concept of the invention, detented positions ofthe shifter finger are associated with predetermined positions of thetransmission, particularly the neutral state and/or a bias-free positionin which a gear is engaged and/or at least one position within theselector track where a shift track branches off, or other characteristicpositions of the transmission.

According to a particularly preferred embodiment of the invention, thecurrent-monitoring function is performed on the total current of thecontrol device and/or a current inside the shifter motor and/or thepower current supplied to the shifter motor and or a current inside theselector motor and/or the power current supplied to the selector motor.

A highly preferred embodiment of the inventive method provides that thetotal current of the control device is monitored, but that the controldevice supplies current only to the actuator device alone and/or only tothe shifter motor alone and/or only to the selector motor alone duringthe time period that is being monitored or evaluated.

Preferably, the current supplied to other consumer devices in thevehicle is measured in accordance with a predetermined characteristicand taken into account in the evaluation of the overall current balance.

As a preferred concept, the current as a function of time is used undercertain conditions to detect when the shifter finger has reached the endpoint of a lateral constraint, for example when the shifter finger movesout of a shift track into the selector track. To make this detectionpossible, the shifter motor and the selector motor are both under powerduring the movement in the shift track, but as long as the shifterfinger is prevented from moving in the selector direction, the selectormotor is stalled and its current flow is therefore increased. As soon asthe shifter finger has reached the selector track and is thus free tomove in the selector direction, the current decreases. The decrease inthe total current can serve as an indication that the shifter finger hasreached the selector track.

According to a particularly preferred embodiment of the invention, theshifter motor is switched off or, in more general terms, the actuationin the shift direction is terminated after detecting that the shifterfinger has reached the selector track.

Also among the preferred concepts, the actuation in the shift directionmay be continued for a predetermined time period or a predetermineddistance after the shifter finger has reached the selector track.

With particular preference, the switch-off point in the shift directionis adapted to the geometry of the selecting/shifting track pattern aswell as to the geometry of the shifter finger. With special preference,after reaching the selector track, the shifter finger is brought into aposition in which it can move in the selector track with a minimalamount of friction and/or without touching the lateral boundaries of theselector track.

According to a particularly preferred embodiment of the invention, afterdetecting that the shifter finger has reached the selector track, it ismoved to a predetermined position in the selector direction. Accordingto the invention, the predetermined position is a boundary of theselector track, in particular one of the end barriers limiting theselector track in the lengthwise direction.

The move to an end barrier of the selector track can occur immediatelyfollowing the detection that the shifter finger has reached the selectortrack. Also among preferred concepts, the move to an end barrier of theselector track is performed independently of whether or not the arrivalof the shifter finger at the selector track has been detected. As aparticularly preferred concept of the invention, the move to the endbarrier of the selector track serves to make an adjustment to theposition sensor device in the selector direction. This procedure may beused, e.g., in a case where the position-sensor device for the shiftdirection is working correctly, but the detection in the selectordirection is incorrect or has failed.

In accordance with the invention, the current of the selector motor orthe total current of the actuator device is monitored while an actuatorforce is applied in the selector direction.

With preference, the selector motor is switched off after an end barrierin the selector direction has been reached. Also as a preferredpossibility, the selector motor is reversed to run in the oppositedirection after reaching an end barrier of the selector track.

Under another preferred concept, the movement of the shifter finger inat least one position is subjected to a local increase or decrease inthe opposing force in at least one of the tracks. Under certainconditions, the local variation in the opposing force can manifestitself by an increase or decrease in the actuator current, so that therespective position can be detected by monitoring and evaluating thecurrent.

A local variation in the opposing force can be effected in particular bydetents at intermediate positions between the end stops of a track. Morespecifically, a component coupled to the shifter finger can be equippedwith a detent or can be moved into a detented position.

As a practical embodiment of the preceding concept, a second shifterelement, in particular a shifter shaft or shifting rod may have asurface profile with depressed and/or raised surface portions. A feelercontact element biased by a spring force follows the profile contour orexerts a force against the contour as the second shifter element movesin relation to the contact feeler element. This creates a variable forceopposing or assisting the movement of the second shifter element,dependent on the location where the contact feeler element is positionedon the profile, and also dependent on the direction of movement of thesecond shifter element. For example, a profile depression is arranged inat least one fully engaged and bias-free gear position and/or in theneutral position and/or at predetermined positions of the selector trackwhere at least one shift track branches off.

Following is an example of how a detent arrangement affects the actuatorcurrent of a shifter shaft that performs gear shifts through angular aswell as axial movements. A single profile depression can be used todetect a position relative to both the shift direction and the selectordirection. For example, the profile depression can be arranged at aspecific point on the shifter shaft so that the contact feeler elementengages the low point of the depression when the shifter finger is at anintersection between the selector track and a shift track.

The foregoing example is used only to illustrate special possibilitiesof the invention without limiting the scope of the invention in any way.A device where the resistance to the movement of a shifter element isused may also be configured in other ways. Furthermore the location ofthe movement-opposing or -assisting feature can also be arranged atother essentially arbitrary locations of the selecting/shifting trackarrangement. Also, a substantially arbitrary number of differentmovement-opposing or -assisting features can be employed in anarrangement according to the invention.

As the shifter shaft is moved axially or rotated about its longitudinalaxis in the process of selecting and shifting, the contact feelerelement will in certain phases move towards a profile depression.

When the selector- or shifter motor is started up, an initial surge inthe motor current can be detected, manifesting itself as a peak in thetime profile of the current. Subsequently, the current will settle andstay at an essentially constant level until the contact feeler elementreaches the profile depression, unless there are other factorsinfluencing the current. Examples of such other influence factorsinclude for example stall conditions where the shifter finger is actedon by a motor, but is constrained by a track boundary.

When the contact feeler element enters the profile depression, in thiscase a bowl-shaped formation, the spring-biased contact feeler elementfollows the down slope of the bowl. At first, the contact feeler elementmoves closer to the central axis of the shifter shaft. After passingthrough the bottom of the bowl, the contact feeler element (which staysin place while the shifter shaft moves) is pushed back again against thespring force. The interactive force between the contact feeler elementand the profile surface is perpendicular to the profile surface at thecontact point. Thus, there is a force component assisting the movementin a first phase where the contact feeler element moves towards thebottom of the bowl and opposing the movement in a second phase where thecontact feeler element moves away from the bottom of the bowl.Corresponding to the amount of the total force required to maintain themovement, the motor current decreases in the first phase and increasesagain in the second phase. Thus, a local dip followed by a rise occursin the profile of the actuator current. The low point of the current canbe used to detect when the contact feeler element is at the detent orlow point of the bowl-shaped depression. As the detent depressioncorresponds to a certain position of the shifter finger within theshifting/selecting track pattern, it is therefore possible to detect aposition of the shifter finger based on the actuator current.

The foregoing concept can be used to detect for example when a gear issettled into an engaged position, or when the transmission is in theneutral position.

According to a particularly preferred embodiment of the invention, theforegoing concept is used in a such a way that there is a change in theforce that opposes the movement of the shifter finger in at least oneplace between the end stops of a track, and the current profile and/orthe change in the opposing force is used to identify which track theshifter finger is moving in. As a preferred possibility, when theshifter finger is actuated in the shifting direction, the arrival at theselector track can be detected from the actuator current. Specifically,a depression in the surface profile would be arranged at theintersection of a shifting track with the selector track. The respectiveshifting track will preferably have additional profile depressions,which can be detected from the variations in the actuator current as theshifter finger moves along the shifting track. Based on the pattern ofdepressions detected, it will be possible to detect the position of theselector track.

The foregoing concept of the invention is advantageous insofar as itallows the arrival at the selector track to be detected by actuating theshifter finger in the shifting direction only.

According to a particularly preferred embodiment of the invention,different tracks, and especially different shifting tracks, can beidentified or distinguished from each other by monitoring and evaluatingthe actuator current.

Under the invention, it is in particular envisaged that each shiftingtrack be distinguished by a characteristic number of profile depressionsand/or profile peaks or detents. As the shifter finger moves through theshifting track, the profile depressions manifest themselves throughlocal decreases followed by increases in the time profile of thecurrent. Based on the number of profile depressions detected in thismanner when moving through a shifting track, the respective shiftingtrack can be positively identified and distinguished from other shiftingtracks without the need for measuring signals of a displacement sensor.

The invention proposes the concept of detecting local or transientchanges in the force opposing the movement of the shifter finger throughthe detection of local or transient extremes in the current.

In particular, such extremes include maxima and minima.

In particular, an increase followed by a decrease in the opposing force,as would occur at a profile peak, manifests itself as a local ortransient peak followed by a dip in the actuator current. A decreasefollowed by an increase in the opposing force, as would occur at aprofile depression, manifests itself as a local or transient dipfollowed by a peak of the actuator current.

In accordance with a particularly preferred embodiment of a methodaccording to the invention, certain gear positions are detectedaccording to a predetermined characteristic relationship, particularlyas part of an emergency procedure. Particularly preferred is a conceptwhere the transmission does not shift through all of the gears whenperforming the emergency procedure.

In particular, the invention proposes the concept for an emergencyprocedure to shift into gear positions in shift tracks that aredistinguished by an end stop, detent, or other movement-resistingfeature in the selector track at the point where the respective shifttrack branches off from the selector track.

A typical case in point is the double-H shift pattern, i.e., ashifting/selecting track arrangement with three selector track positionswhere shift tracks take off from the selector track, so that thetransmission can be shifted into a total of six different gears. Underan emergency procedure as described above, the transmission would moveinto the shifting tracks that branch off from the end point of theselector track. Typically, this means shifting into first, second, fifthand reverse gears. It is particularly preferred if the transmission alsofinds and positively identifies the neutral position during thisemergency procedure. In a particularly preferred embodiment for a shiftpattern where fifth and reverse gears branch off at essentially the sameselector position, the transmission will search for neutral, firstand/or second, and reverse gears.

A four-track pattern is defined as a shifting/selecting track patternwhere reverse, first, third and fifth gears lie in parallel shift tracksin the upper half of the pattern, and where second and fourth gears lieopposite first and third, respectively, in the lower half of thepattern.

Preferably, a detent or resistance barrier is arranged in the selectortrack between the branch-off point for first/second and the branch-offpoint for reverse gear.

In the search procedure, the shifter finger is moved towards thisresistance barrier with a limited actuator force, so that the barrier,e.g., in the form of a profile peak, cannot be overrun withoutincreasing the actuator force. This resistance barrier, which can alsohave the form of a profile depression, may likewise be used to find andmove into the first and second gear positions under the emergencyprocedure.

As a preferred feature for an emergency procedure, after the shifterfinger has reached an end of the selector track and is about to movefrom there into a shift track, the shifter finger is subjected to acontinuing but preferably small force in the selector direction towardsthe end stop, to ensure that the shifter finger finds its way into theshift track.

In accordance with a particularly preferred embodiment of the invention,when searching for a predetermined gear position and before the shifterfinger has entered the respective shift track, an appropriate step istaken to confirm that the shifter finger is in the correct selectorposition from which the targeted shift track branches off. Thisconfirmation can be achieved, e.g., by taking the direction of travelinto account in which the shifter finger was moving prior to reachingthe branch point on the selector track.

For example, in a double-H shift pattern where the shifter finger hasreached an end stop of the selector track while traveling with a firstsense of direction, it can be confirmed that the end stop for thattraveling direction belongs to the branch point for first/second gears.If the shifter finger has been moving in the opposite direction, it canbe confirmed that the end stop for that traveling direction belongs tothe branch point for reverse/fifth gears.

While the transmission searches for the different gear positions, thecurrent is monitored, so that the end stops, detents, or other barrierfeatures can be detected from the behavior of the current. The movementof the shifter finger can be directed dependent on the behavior of theactuator current, so that the shifter finger is moved in a shift-trackdirection when the correct position has been reached.

In accordance with a particularly preferred embodiment, the inventiveconcepts are used in a phase of gear engagement, particularly under anemergency procedure, to detect the point of synchronization and/or theunlocking of the synchronization and/or the arrival at the end positionof the shift track, and or the unbiased, engaged gear position.

The point of synchronization in the present context means the positionat which the gears of a particular gear level are about to enter intomeshing engagement. At this point, it will be necessary in certainsituations for one of the gears to turn by a small amount in relation tothe other before the tooth profiles can mesh with each other.

A completed synchronization or unlocked condition in the present contextmeans a state where the gears of the ratio level to be engaged are in aposition where the tooth profiles can move into engagement without thelateral tooth flanks blocking each other, which would constitute a kindof lock.

The invention proposes the concept of detecting one or more of theaforementioned positions or events on the basis of the actuator current.

For example, a point of synchronization can be detected by the fact thatgears whose lateral flanks have come into mutual contact can undercertain conditions at least temporarily prevent the gears from meshingwith each other, so that further movement is blocked at least until theblockage is released. This locked condition causes a momentary increasein actuator current. When the current returns to a lower level, thisindicates that the blocked condition has ended.

When a renewed increase in actuator current is detected after apredetermined time interval, this can be used as an indication that theshifter finger has reached the end of the shifting track.

Preferably, the actuation of the first shifter element in the shiftingdirection for shifting into first gear is terminated when the end of theshifting track has been detected.

According to a particularly preferred embodiment of the invention, theactuation in the shifting direction is continued for a predeterminedtime period after a resistance barrier has been detected in the shiftingtrack. This has the purpose of distinguishing temporary barriers such asa blocked synchronizer process from permanent barriers such as the endof the shifting track. This distinction is particularly important if atthe time of putting the transmission in gear, the tooth profiles happento be mutually positioned so that their lateral tooth flanks are notinterfering with each other, in which case no blockage occurs.

According to a particularly preferred embodiment of the invention, ashake-down phase is performed when the end stop of a shifting track hasbeen detected in the course of shifting the transmission into gear.

A shake-down phase in the present context means a pulsating actuation ofa movable element of the transmission. This can be achieved by drivingthe selector- and or shifter motor with voltage pulses of alternatingpolarity for a predetermined amount of time. The alternating pulses arefor example in a range between 0.3 and 5 volts. Preferred are pulsesbetween 0.3 and 3 volt, with special preference for pulses between 0.5and 2 volt.

The shake-down causes the shifter finger and/or a component coupled tothe latter to settle into an unbiased (force-free) equilibrium position.

Subsequently, the actuation of the shifter finger is terminated after apredetermined time period has elapsed.

As a preferred concept of the invention, after the unbiased position hasbeen found, a plausibility test is performed whether the actuallyengaged gear is the one that was intended. This can be established bychecking whether the ratio between the engine rpm rate and a wheel rpmrate correlates correctly with the intended transmission ratio.

According to a particularly preferred embodiment, a shake-down phase isperformed when the transmission is put into neutral, so that the shifterfinger and/or transmission components coupled to the latter will settleinto an unbiased condition.

A process according to the inventive method is started with preferenceafter detecting certain kinds of faults of the sensor device and/or theactuator device and/or the control device. A fault in the presentcontext means in particular any impairment of functionality. A fault inthe present context can also mean a loss of confidence in the positionvalues determined by the position sensor device. The loss of confidencecan occur, for example, if blockages of shift movements occur atunexpected times or in unexpected positions.

According to a particularly preferred embodiment of the invention, adetermination of a position through one of the procedures of theinventive method may under certain conditions be performed as aredundant measure, for the purpose of adapting the position sensordevice or its output values to changes in the system.

According to a particularly preferred embodiment of the invention, aredundant position information is used to control the transmission onlyif the values generated by the position sensor device have positivelybeen found to be faulty.

The invention provides a further operating method for a vehicletransmission in which predetermined shift positions, in particular atleast one position of full engagement of a gear and/or at least oneposition in the selector track, are associated with profile depressionsthat are arranged on a movable element. The method includes thefollowing steps:

a) Under predetermined conditions and in accordance with a predeterminedcharacteristic, the transmission is actuated to seek a position that isassociated with a profile depression.

b) A shake-down or vibratory movement is carried out to settle the firstelement (or another element coupled to the latter) into an essentiallyunbiased, force-free position, after detecting that the contact feelerelement has substantially arrived at the depression. The shake-downmovement is generated by applying an alternating pulsating force to atleast one shifter element, so that the shifter element is at least oncepushed quickly back and forth.

The invention provides a further method of detecting a change inposition, or detecting a position relative to a reference point in atransmission. This further method includes the step of emulating atleast one actuator device by means of a model that is incorporated inthe control device. This method, too, applies to a transmission that hasdifferent rotary transfer ratios between an input- and output shaftcorresponding to the different shift positions.

Shifting the transmission into one of the positions requires a movementin the shift direction and in some cases also in the selector direction.The movement in the selector direction is controlled by a firstelectrically controlled actuator device, and the movement in the shiftdirection is controlled by a second electrically controlled actuatordevice. The first and/or second actuator device is equipped with adisplacement sensor device, and the transmission has at least oneelectric control device to control the actuator devices.

According to a proposed embodiment of the invention, the actuator devicefor the selector movement and/or shift movement is emulated in thecontrol device, e.g., through a model of a servo-control loop.

According to a preferred embodiment of the aforementioned method, thecommand signal by which a position-control unit directs the movements ofan actuating device is used also as input for the servo model thatemulates the actuator device. As an example, the command signal can bean analog voltage signal.

The output signal delivered by the emulator model is preferably anequivalent counterpart to the signal of the displacement sensor device.The displacement sensor can be realized, e.g., by an incrementalposition sensor, in which case the output signal of the emulation modelis preferably made available in terms of angular increments or in radianunits.

It is particularly advantageous if the emulation model of an actuatordevice is based on characteristic variables or design data and/or atleast one measured quantity of the actuator device. If the latterconsists of a rotary drive mechanism, the characteristic variables canconsist in particular of an rpm rate and/or a rotary acceleration, or ofvariables from which a rotary speed or acceleration can be calculated.If an electric motor such as a DC motor is used as a drive source, thecharacteristic design data used in the emulator model can, e.g., consistof the moment of inertia of the rotor, the electrical resistance of therotor, and/or a torque constant. For a measured quantity, it isadvantageous to use an rpm-dependent friction of the motor.

The use of an emulator model of the actuator device represents aparticularly advantageous means for detecting a failure and/ormalfunction of the displacement sensor. In practice, the faultrecognition is based on calculating and evaluating the differencebetween the respective output signals of the displacement sensor deviceand the emulator model. A fault is indicated if the difference exceeds agiven threshold. It is practical to set the sensitivity of the faultrecognition through an appropriate selection of the threshold value,preferably taking the accuracy of the emulator model and possibly otherfactors into account. In one advantageous embodiment, an on/offhysteresis is used for an indicator flag signaling a fault ormalfunction.

If a failure and/or malfunction has been recognized, appropriatemeasures are taken such as, e.g., initiating a special strategy foroperating faults and/or making an entry into a fault memory.

In regard to a special strategy for operating faults, reference ishereby made to the German Patent Application Publication DE 199 00 820,the content of which is expressly incorporated by reference in thepresent patent application.

According to a further concept of the invention, an adaptation of themodel is advantageously performed at a time when the displacement sensordevice is fully functional. In case there is a difference between theoutput signals of the emulator model and the displacement sensor, theemulator model is adjusted to produce an output that more closelymatches the signal of the displacement sensor.

The invention provides a further embodiment of a method which isparticularly advantageous for controlling a transmission without thedisplacement sensor device that is part of the preceding embodiment. Inthis case, the displacement and/or position relative to a fixed point ofthe transmission is determined by the emulator model alone.

The scope of the invention also includes control devices that areequipped with a signal-evaluating capability and are operable to performany of the methods of the foregoing description. Specifically, suchcontrol devices electrically control an actuator device that applies anactuating force to a first and/or second shifter element of atransmission, where the first shifter element is movable in aselecting/shifting track arrangement and where the position of at leastone of the shifter elements can be detected by a position sensor.

Further included under the scope of the invention are transmissions ofthe type described above with at least a first shifter element that ismovable in selecting/shifting track arrangement, and at least one secondshifter element, an electrically controlled actuating device for atleast one of the shifter elements, at least one control device for theactuator device, at least one position sensor device to determine theshift position of the transmission at any given time and, in addition, aredundant sensor device performing in certain predetermined situations aredundant determination of the shift position relative to the selectordirection.

The invention further includes any transmission capable of performingone or more of the inventive methods described herein.

As a linguistic formality, where the names of features are connected bythe word “or”, this should be understood in the broadest sense, i.e.,either as a logic type of “or” (one or the other or both) or anexclusive “or” (one or the other but not both), whichever fits thecontext.

The terms “control” and “regulation” and their derivatives are usedherein with a broad range of meanings encompassing closed-loop as wellas open-loop control of devices, functions and processes, including inparticular the DIN (Deutsche Industrie-Norm) definitions for regulationand/or control).

The novel features that are considered as characteristic of theinvention are set forth in particular in the appended claims. Theinventive method itself, however, both as to its mode of operation andits application in a motor vehicle, together with additional featuresand advantages thereof, will be best understood upon perusal of thefollowing detailed description of certain presently preferred specificembodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the invention as described and illustrated areintended to serve as examples only, and no limitations are therebyimplied. The description refers to the attached drawings, wherein

FIG. 1 represents a schematic view of a first vehicle in which theinventive method may be used;

FIG. 2 represents a schematic view of a second vehicle in which theinventive method may be used;

FIG. 3 represents a schematic view of a first shift pattern in which theinventive method may be used;

FIG. 4 represents the shift pattern of FIG. 3 correlated with a surfaceprofile on a shifter shaft;

FIG. 5 represents a schematic view of a second shift pattern in whichthe inventive method may be used;

FIG. 6 represents a first example of a signal profile of acharacteristic electrical variable that can be used to detectpredetermined shift positions;

FIG. 7 represents a second example of a signal profile of acharacteristic electrical variable that can be used to detectpredetermined shift positions;

FIG. 8 represents a first example of a flow chart of a method accordingto the invention;

FIG. 9 represents a second example of a flow chart of a method accordingto the invention;

FIG. 10 represents time profiles of several different characteristicvariables which can be used according to the invention to detectpredetermined shift positions;

FIG. 11 represents a third example of a flow chart of a method accordingto the invention;

FIG. 12 represents a fourth example of a flow chart of a methodaccording to the invention;

FIG. 13 represents a schematic view of portions of a transmission inwhich the method according to the invention can be used;

FIG. 14 represents a schematic view of a shift pattern correlated with afirst signal profile.

FIG. 15 represents a schematic view of a shift pattern correlated with asecond signal profile;

FIG. 16 represents an arrangement analogous to FIG. 13, with a differentkind of redundant displacement sensor;

FIG. 17 represents an example of a block-diagram model of an actuatordevice; and

FIG. 18 represents an example of a flow chart of an error-detectionstrategy.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 gives a schematic view of a vehicle 1 with a drive unit 2 such asa motor or combustion engine. The power train of the vehicle furthercontains a torque-transmitting device 3 and a transmission 4. Theillustrated example shows the torque-transmitting device 3 arranged inthe torque flow path between the engine and the transmission, so thatthe driving torque generated by the engine is passed on by way of thetorque-transmitting device 3, the transmission 4, the drive shaft 5, andthe driving axle 6 to the wheels 6 a.

The torque-transmitting device 3 is configured as a clutch, such as afriction clutch, laminar disc clutch, magnet powder clutch, or converterbypass clutch. The clutch may be of the self-adjusting,wear-compensating type. The transmission 4 is shown as a manual shifttransmission in which the transmission ratio is changed in steps.However, under the concept of the invention, the transmission may alsobe an automated shift transmission in which the shifting process isautomated by means of at least one actuator. The term “automated shifttransmission” further means an automated transmission of a type wherethe tractive force is interrupted during gear shifts and where theshifting from one transmission ratio to another is performed by means ofat least one actuator.

It is also possible to use a conventional automatic transmission of thetype that works without interrupting traction during gear shifts and isnormally based on planetary gear stages.

As a further possibility, a transmission with a continuously variablerotary transfer ratio, such as for example a cone-pulley transmission,may be employed in embodiments of the invention. If a conventionalautomatic transmission is used, the latter may be equipped with atorque-transmitting device 3, e.g., a clutch or friction clutch,arranged at the output side of the transmission. The torque-transmittingdevice can further be configured as a start-up clutch and/or as areverse-gear clutch and/or as a safety clutch in which the magnitude ofthe transmittable torque can be controlled at a targeted level. Thetorque-transmitting device can be a dry friction clutch, or a so-calledwet-running friction clutch that runs in a fluid, or it may consist of atorque converter.

The torque-transmitting device 3 has an input side 7 and an output side8. A torque is transmitted from the input side 7 to the output side 8through a contact force that is applied to the clutch disc 3 a by meansof the pressure plate 3 b, the diaphragm spring 3 c, the release bearing3 e, and the flywheel 3 d. The force is generated by an actuator pushingor pulling the release lever 20.

The torque-transmitting device 3 is controlled by means of a controlunit 13 which may be configured as a control device with an electronicmodule 13 a and an actuator 13 b. In another advantageous embodiment,the actuator and the electronic module may also be accommodated in twoseparate subassembly units or housings.

The control unit 13 may contain the electronic circuits for the controlas well as for the power supply of the electric motor 12 of the actuator13 b. This has the advantage that only one compact portion of space isneeded for both the actuator and the electronics. The actuator consistsof a motor 12, typically an electric motor driving a hydraulic mastercylinder 11 through a gear mechanism such as a worm gear mechanism, aspur gear mechanism, a crank mechanism, or a threaded spindle mechanism.The master cylinder may be driven directly or by way of a rod linkage.

The movement of the output element of the actuator, i.e., of the piston11 a of the master cylinder 11, is detected by a clutch travel sensor 14which senses a position, or the speed or acceleration of a change inposition, of an element whose displacement, speed or acceleration is indirect proportion to the displacement, speed or acceleration of theclutch. The master cylinder 11 is connected through a pressure conduit9, normally a hydraulic line, to the slave cylinder 10. The outputelement 10 a of the slave cylinder is coupled to the release lever orrelease element 20. Thus, a movement of the output element 10 a of theslave cylinder 10 causes the release element 20 to be moved or tilted toeffect a controlled variation of the amount of torque that istransmitted by the clutch 3.

The actuator 13 b that controls the torque-transmitting device 3 may bebased on a pressure-propagation principle, using a master cylinder andslave cylinder communicating through a pressure medium. The pressuremedium can be a hydraulic fluid or a pneumatic medium. The mastercylinder may be driven by an electric motor 12 that is electronicallycontrolled. However, instead of an electric motor, the driving elementof the actuator 13 b may also be based on another drive source, e.g.,driven by hydraulic pressure. It is also conceivable to use magnet-basedactuators to set a position of an element.

The amount of torque transmitted through a friction clutch is controlledto a targeted level by applying pressure on the friction linings of theclutch disc between the flywheel 3 d and the pressure plate 3 b. Theforce that is exerted on the pressure plate and on the friction liningsis controlled by the position of the release element 20, whereby thepressure plate is moved to or set and held at any position between twoend positions. One end position represents a fully engaged condition ofthe clutch, and the other end position represents a fully disengagedcondition. To set the transmittable torque at an amount that is lessthan the current engine torque, the pressure plate 3 b is moved to aposition that lies in an intermediate range between the end positions.By controlling the release element 20 to a set target, the clutch can beheld at the targeted position. However, it is also possible to set thetransmittable torque above the level of the current engine torque. Inthis case, the torque generated by the engine is passed on by theclutch, while torque fluctuations, especially abrupt peaks in the torqueflow, are damped and/or isolated.

The control and regulation of the torque-transmitting device furtherrelies on sensors which at least part of the time monitor the relevantfactors and provide the status data, signals and measurement values thatare necessary for the control and are processed by the control unit. Thelatter may also have communication lines to other electronic units suchas, e.g., an electronic engine control unit, or an electronic control ofthe anti-lock braking system (ABS), or an anti-slip regulation (ASR).The sensors detect, for example, rpm rates of the vehicle wheels or ofthe engine, the position of the gas pedal, the position of the throttlevalve, the currently engaged gear level of the transmission,driver-generated inputs that indicate an impending gear change, andother characteristic information specific to the vehicle and theoperating situation.

FIG. 1 shows a throttle valve sensor 15, an engine rpm sensor 16, aswell as a vehicle speed sensor 17, which relay measurement data andinformation to the control device. The electronic unit, such as acomputer unit that is part of the control unit 13 a, is processing theincoming data and issues control commands to the actuator 13 b.

The transmission is configured as a step-shifting transmission, in whichthe transmission ratio is shifted in discrete, fixed steps by means of ashift lever. The shift lever may operate or actuate the transmissiondirectly. There is further at least one sensor 19 b arranged at theshift lever 18 of the manual shift transmission, which serves to detectwhen the driver intends to shift gears and/or which gear is currentlyengaged, and to relay the information to the control device. The sensor19 a is connected to the transmission and serves to detect the currentlyengaged gear of the transmission and/or to detect a condition thatindicates that the driver is about to shift gears. The detection of thedriver's intent to shift gears can be realized through the use of atleast one of the sensors 19 a, 19 b, if the sensor is a force sensorthat responds to a force acting on the shift lever. Alternatively, thesensor could also be a position sensor or displacement sensor, in whichcase the control unit would recognize an intent to shift gears from adynamic change of the position signal.

The control device is at least part of the time in signal communicationwith all of the sensors and evaluates the sensor signals and input datawhich, in their totality, are referred to as the current operating pointof the torque transfer system. Based on the operating point, the controldevice issues control and regulation command signals to the at least oneactuator. The drive element 12 of the actuator, such as an electricmotor, operates under the command of the control unit that controls theactuation of the clutch by means of a command signal that depends on themeasurement values and/or the system input data and/or signals of thesensors. The control device has a control program in the form ofhardware and/or software, which evaluates the incoming signals andcalculates or determines the output quantities based on comparisonsand/or functions and/or characteristic data arrays or curve fields.

The control unit 13 is advantageously equipped with units or modules forthe determination of torques, gear positions of the transmission,amounts of slippage in the clutch, and/or different operating states ofthe vehicle, or there are signal connections from the control unit 13 toat least one of the aforementioned modules. The modules or units may beimplemented in the form of control programs in hardware and/or software.As a result, the incoming sensor signals allow a determination of thetorque of the drive unit 2 of the vehicle 1, the gear position of thetransmission 4, the amount of slippage in the torque-transmittingdevice, as well as the current operating state of the vehicle. Thegear-position determining unit detects which gear is currently engagedbased on the signals from the sensors 19 a and 19 b. The sensors arecoupled to the shift lever and/or to internal mechanical elements of thetransmission such as, e.g., a central shifting shaft or shifting rod, todetect the position or movement of these elements. There can further bea gas pedal sensor 31 arranged at the gas pedal 30 to detect theposition of the latter. A further sensor 32 may consist of a binaryon/off switch to indicate when the engine is idling, i.e., the switch 32is on when the gas pedal is not being depressed, and it is off when thegas pedal is being actuated. The gas pedal sensor 31, in contrast to theon/off switch 32, provides a quantitative signal representing the degreeof actuation of the gas pedal.

Further in FIG. 1, a brake-actuating element 40 is shown which serves toapply the service brake or the parking brake. This can be a brake pedal,a hand-brake lever, or a hand- or foot-operated actuating element of theparking brake. At least one sensor 41 is arranged at the actuatingelement 40 to monitor the actuation of the latter. The sensor 41 may bea digital sensor, e.g., a binary switch for detecting whether theactuating element is in an applied or non-applied state. This sensor maybe connected to a signal device such as a brake indicator light to alertthe driver that the brake is applied. This arrangement can be used forthe service brake as well as for the parking brake. However, the sensorcan also be configured as an analog sensor, e.g., as a potentiometerthat measures the degree of displacement of the actuating element. Thissensor, likewise, can be connected to an indicator signal.

FIG. 2 gives a schematic view of a power train of a motor vehicle with adrive unit 100, a torque-transmitting device 102, a transmission 103, adifferential 104, drive axles 105, and wheels 106. Thetorque-transmitting device 102 is arranged at or connected to a flywheel102 a. The latter as a rule carries an external tooth profile 102 b thatserves to start the engine. The torque-transmitting device has apressure plate 102 d, a clutch cover 102 e, a diaphragm spring 102 f,and a clutch disc 102 c with friction linings. The clutch disc 102 c isinterposed between the pressure plate 102 d and the flywheel 102 a andmay be equipped with a damping device. An energy-storing device such asa diaphragm spring 102 f pushes the pressure plate axially towards theclutch disc. A clutch-actuating element 109 such as a hydraulicallyactuated concentric slave cylinder is used to actuate thetorque-transmitting device. A release bearing 110 is arranged betweenthe concentric slave cylinder and the prongs of the diaphragm spring 102f. As the release bearing is moved along the axial direction, it pushesagainst the diaphragm spring and thereby disengages the clutch. Theclutch may be configured either as a push-actuated clutch or apull-actuated clutch.

The actuator module 108 belongs to an automated shift transmission andincludes the actuator unit for the torque-transmitting device. Theactuator module 108 operates internal shifter elements such as, e.g., ashift-actuating cylinder or a rod mechanism, or a central shifter shaftof the transmission. The actuation may work in a manner where the gearscan be engaged and disengaged in sequential order or in an arbitraryorder. The clutch-actuating element 109 is operated by way of theconnection 111. The control unit 107 is connected to the actuatorthrough the signal line 112. The control unit 107 is further connectedby signal lines 113 to 115. The signal line 114 carries incomingsignals. The line 113 carries command signals issued by the controlunit. The connection 115, consisting for example of a data bus,exchanges signals with other electronic units.

To put the vehicle in motion or to accelerate the vehicle from astationary or slow rolling condition, the driver has to use only the gaspedal 30, as the controlled or regulated automatic clutch actuationcontrols the amount of transmittable torque of the torque-transmittingdevice. The degree of depression of the gas pedal is detected by the gaspedal sensor 31, and the control unit will accordingly implement a moreor less forceful or rapid start-up acceleration. The sensor signals fromthe gas pedal are used as inputs for the control of the start-up phaseof the vehicle.

In a start-up phase, the amount of transmittable torque is set as acontrol target by means of a given function or on the basis ofcharacteristic curves or curve fields that may be functions of theengine rpm rate. The latter may in turn be dependent on other quantitiessuch as the engine torque, that are correlated to the engine rpm ratethrough a characteristic relationship.

In a start-up process, essentially from a stationary or crawl-speedcondition, if the gas pedal is actuated by an amount a, the enginecontrol device will direct the engine to generate an engine torque of acertain magnitude. The control unit of the automated clutch actuation 13controls the transmittable torque of the torque-transmitting device inaccordance with given functions or characteristic curve fields, so thata stationary equilibrium sets in between the engine torque and theclutch torque. The equilibrium is characterized dependent on the gaspedal displacement a by a specific start-up rpm rate, a start-up torquegenerated by the engine, a specific amount of transmittable torque ofthe torque-transmitting device, and a specific amount of traction torquedelivered to the drive wheels. The functional relationship between thestart-up engine torque and the start-up rpm rate will subsequently bereferred to as the start-up characteristic. The gas pedal displacement ais proportionate to the aperture of the throttle valve of the engine.

Further in FIG. 2, a brake-actuating element 120 is shown which servesto apply the service brake or the parking brake. This can be a brakepedal, a hand-brake lever, or a hand- or foot-operated actuating elementof the parking brake. At least one sensor 121 is arranged at theactuating element 120 to monitor the actuation of the latter. The sensor121 may be a digital sensor, e.g., a binary switch for detecting whetherthe actuating element is in an applied or non-applied state. This sensormay be connected to a signal device such as a brake indicator light toalert the driver that the brake is applied. This arrangement can be usedfor the service brake as well as the parking brake. However, the sensorcan also be configured as an analog sensor, e.g., as a potentiometerthat measures the degree of displacement of the actuating element. Thissensor, likewise, can be connected to a signal indicator device.

FIG. 3 illustrates an example of a shift pattern 300 with a selectortrack and shift tracks, which is part of an arrangement according to theinvention and also serves to give a clearer description of a methodaccording to the invention.

The selecting/shifting track pattern 300 in FIG. 3 has the shape of adouble-H. The shift tracks 302, 304, 306, 308, 310 belong to the forwardgears one through five, respectively, and the shift track 312 belongs tothe reverse gear. The shift tracks are connected by the selector track314.

The method according to the invention serves to detect when the shifterfinger is positioned at predetermined end stops or predetermined gearpositions. The method can be used, e.g., as an emergency strategy duringa temporary failure of a displacement measuring device. It can also beused to calibrate the displacement measuring device in a procedure thatis performed as a safety measure at predetermined time intervals.

A method according to the invention will now be discussed in which thegear positions or the end positions of the respective shift tracks aredetermined in sequence for first, second, fifth and reverse gear. Thescope of preferred embodiments also includes other orders of sequence.

The method is discussed for an exemplary case, where the shifter finger(not shown in the drawing) is positioned at the outset in the selectortrack 314. The starting position of the shifter finger in the selectortrack 314 may have been detected by an inventive method that is notdescribed in detail within the context of FIG. 3.

The shifter finger (not shown) is pushed by a selector motor along thedouble arrow 316 towards the end stop 318 of the selector track. Duringthis activity, the current of the selector motor or the total current ofa control device directing the selector motor is monitored. Forsimplicity's sake, the following explanation will consistently refer tothe total current of the control device, although the invention includesthe possibility of detecting the currents of the shifter motor andselector motor separately.

During a start-up phase of the selector motor, the current profile ofthe control device will show a temporarily increased current flow whichis due to the start-up current of the selector motor. After the startingphase, the current falls to a lower level and stays essentially constantuntil the shifter finger has reached the end stop 318 of the selectortrack. After arriving at the end stop 318, the shifter finger continuesto be pushed against the end stop by the selector motor, so that thestalled condition can be detected from a strong increase in the current.The position at the end stop 318 can be distinguished from the end stop320 based on the direction of movement of the shifter finger. The senseof direction can be determined, e.g., by monitoring the signal of anincremental displacement sensor which is used to detect the motion ofthe shifter finger. As an alternative, a profile indentation or a detentcan be arranged at a short distance from the end stop 318 or at anappropriate place of the shifter shaft, which will manifest itselfthrough a local variation of the current profile that will occur at theend stop 318 but be absent at the end stop 320.

After the arrival of the shifter finger at the end stop 318 has beendetected, the selector motor is switched off, whereby a negative currentis induced which subsequently rises to the zero level. The end stop 318can also be used as a reference for the calibration of the displacementmeasuring device in the selector direction. As an alternative toswitching off the selector motor, the latter could remain energized toexert a very small force on the shifter finger in the direction of theend stop 318 to ensure that the shifter finger is in fact being movedalong the shift track 302. For the movement in the shift track 302, theshifter motor pushes the shifter finger in the direction towards the endstop 330 of the shift track 302. Initially, this will cause a start-upsurge of the current which manifests itself as a peak in the currentprofile. Subsequently, the current decreases and then remains at asubstantially constant level until the end stop 330 has been reached. Atthe end stop 330 the current profile will at first show an increase asthe shifter motor is stalled by the end stop 330 opposing furthermovement of the shifter finger.

After the arrival at the end stop 330 has been recognized, the shiftermotor is switched off, so that the inductive switch-off current willcause a dip into the negative of the current profile.

Following this, the shifter motor will push the shifter finger in theopposite direction, and the arrival at the end stop 332 will manifestitself by a current increase. The shifter motor is switched off at thispoint, which again causes an inductive switch-off current that willmanifest itself through a negative transient in the current profile.Next, the shifter motor is energized to push the shifter finger in theopposite direction, causing another start-up surge (transient peak) inthe current, whereupon the current level decreases to a substantiallyconstant level. After the selector track 314 has been reached, theshifter motor is switched off and the selector motor is energized topush the shifter finger in the direction towards the selector-track endstop 320. The arrival at the end stop 320 is again detected from astrong rise in the current. In analogous manner, the movement iscontinued to the end stop 334 of the shift track 310 and subsequently tothe end stop 336 of the shift track 312. The positions at the end stops330, 332, 334, 336 are detected and used for the calibration of thedisplacement sensor device.

FIG. 4 illustrates the same shifting/selecting track pattern 300 with aschematic representation of a shifter shaft 350 which in accordance withthe movement of the shifter finger is moved axially in the shifterdirection symbolized by the double-headed arrow 352 or rotated about itsaxis in accordance with a movement of the shifter finger in the selectordirection.

A contour or detent profile 354 is provided on the shifter shaft 350with profile peaks 356, 358 and profile depressions 362, 364. At asubstantially fixed position, a spring-biased contact feeler element(symbolized by the arrow 366) pushes against the profile 354. The axialcomponent of the contact force variably opposes or assists the axialmovement of the shifter shaft 350 dependent on the position of thelatter. As a consequence, the actuator current profile, which is beingmonitored during the movement of the shifter shaft 350 or of the shifterfinger (not shown in FIG. 4), shows local extreme values when thecontact feeler element 366 is at one of the profile depressions 360,362, 364. An appropriate arrangement of a surface profile cooperatingwith a contact feeler element 366 can thus be used to detect by way ofthe actuator current profile when the shifter finger is located atpredetermined shift positions or in the selector track.

FIG. 5 illustrates an example of a selecting/shifting track pattern 380which may be part of a transmission in accordance with the invention, orwhich can be used to perform a process according to the invention.

The arrangement of FIG. 5 is also referred to as a four-track pattern,where the four tracks belong to reverse, first/second, third/fourth, andfifth gear, respectively.

A reverse-gear barrier 382 is arranged between the shift track 302/304for first/second gear and the shift track 312 for reverse gear. In thecurrent profile, the reverse-gear barrier 382 manifests itself like anend stop when the shifter finger moves against it, so that the entryinto reverse gear can be detected from the actuator current.

FIG. 6 illustrates an example of a profile graph of the current (inarbitrary units) of a shifter motor that can occur when the shifterfinger moves (as measured in position increments) through a shift trackthat is associated with a detent arrangement as shown in FIG. 4. Whenthe shifter motor is switched on, the current goes through a start-upsurge that manifests itself as a peak in the area 390 of the graph,which is followed by a sharp descent in the area 392. In this phase, theshifter finger is positioned substantially in the surface profiledepression 364 (FIG. 4). The continued movement where the contact feelerelement 366 glides over the profile peak 358 can be detected from thelocal maximum 394 of the current in FIG. 6. This is followed by a markeddecline of the current towards a local minimum value at 396, whichcorresponds to the depression 362 in the surface profile 354 of FIG. 4.The position of the contact feeler element 66 in the depression 362corresponds essentially to a position of the shifter finger in theselector track 314 of the shift pattern of FIG. 4. As the contact feelerelement glides over the surface profile peak 356, the current rises toanother local maximum at 398 and subsequently falls to a local minimum400 as the contact feeler element glides into the surface profiledepression 360. When the shifter finger has reached the end of the shifttrack, the stalled condition of the shifter motor can be detected fromthe strong rise in the current in the area 402 of the graph.

The graph of FIG. 7 represents the total current of a control devicethat can occur when the shifter finger travels along the selector track.When the selector motor starts up, a current surge can be detected inthe area 410 of the graph. During the movement along the selector track,the current remains essentially constant within ±1 measuring unit, asseen in the portion 412 of the graph. At the end stop of the selectortrack, a strong current increase of the current can be detected as shownin the area 414 of the graph.

FIG. 8 represents an example in flow-chart format, where the methodaccording to the invention is used as an emergency procedure to move thetransmission into predetermined positions within the selecting/shiftingtrack pattern and to detect the predetermined positions. The sameprocedure can also be used to adjust or calibrate a displacement sensordevice.

The procedure is started at step 420. In step 422 a shake-down phase isinitiated to ensure that the shifter finger or a movable elementconnected to the latter is settled into an unbiased, force-freecondition.

In step 424, the shifter finger is moved back and forth in the selectordirection. In step 426, a test is performed whether end stops weredetected in step 424. This test is made by measuring the total currentof the control device. If no stops were detected in step 426, theprocess is terminated in step 428. In the affirmative case of step 426,i.e., if end stops were detected, a further test is made in step 430,whether the time interval from detecting one stop to the other wasshorter than a predetermined amount of time. As the process is directedthrough the voltage transmitted by the control device, the fact that thetime interval between opposite end stops was shorter than apredetermined value can be used as an indicator that the shifter fingeris positioned in a shift track. In the negative case of step 430, i.e.,if the time interval between end stops is found to be longer than apredetermined amount of time, this can serve as an indicator that theshifter finger is positioned in the selector track. The method proceedsto step 446, which will be described below after step 444.

In the affirmative case of step 430, i.e., if the time interval isshorter than a predetermined amount, the method continues in step 432,where the shifter finger is moved back and forth in the shift direction.In step 434, a test is performed as to whether or not end stops weredetected in the back-and-forth movement of step 432. As in step 426,this test is based on measuring the total current of the control device.In the affirmative case of step 434, i.e., if end stops were detected, atest is made in step 438, whether the selector track has been found. Thedetection of the selector track can be based, e.g., on a detent at theintersection of the selector track and the shift track which produces acharacteristic response in the total current signal of the controldevice when the shifter finger reaches the selector track.

In the negative case of step 438, i.e., if the selector track was notdetected, a further test is made in step 440 whether the number of timesthat the method failed to detect the selector track exceeds a giventhreshold number. In the affirmative case, the process is terminated instep 442. In the negative case, the method loops back to step 432.

If step 438 indicates that the shifter finger has reached the selectortrack (i.e., the contact feeler element has reached the correspondingdetent position of the surface profile), a vibratory or shake-down phaseis initiated in step 444 to ensure a settled, bias-free position in theselector track. Subsequently, in step 446, the shifter finger is movedin the selector track direction towards the shift track of first/secondgear. As mentioned above, step 446 is also performed after a negativeoutcome of step 430.

Next, a test is made in step 448 by measuring the total current of thecontrol device, whether or not a stop was detected in the selectortrack. In the negative case, the method loops back to step 424. In theaffirmative case, a shake-down process is performed in step 450 tosettle the shifter finger in a defined position in the selector trackbetween first and second gear.

Step 452 collectively represents the continuation of the method in whichthe shifter finger is moved under voltage control into the positions offirst and second gear as well as fifth and reverse gear, whilemonitoring the current during the movement.

FIG. 9 illustrates another application of the inventive method to take agear out of engagement and to detect when the selector track has beenreached.

In step 460, the shifter finger is actuated by forces in the shiftdirection as well as the selector direction. The force in the shiftdirection is oriented towards the selector track. The total current ofthe control device is monitored over time. In step 462, the totalcurrent is found to be decreasing. This serves as an indicator that theshifter finger, which was previously constrained by the shifter track,has left the latter and has become free to move in the selector track.

In step 464, the shifter motor is switched off, after a small voltagepulse may have been applied in the shift direction (optional).

FIG. 10 represents time graphs of different characteristic variablesduring a time phase when the inventive method is being performed. Inparticular, FIG. 10 serves to explain how the invention proposes todetect positions of the shifter finger based on the time profiles ofcertain characteristic electrical variables.

The three graphs of FIG. 10 represent the voltages 470 and 472 of theselector motor and the shifter motor, respectively, the total current474 delivered by the control device, and the displacement components 476and 477 of a movable element in the shift and selector directions,respectively. The movable element is in particular a shifter finger.

In the left-hand portions of the time graphs 470, 472, 474, 476, 477, asindicated by the broken line 480 and the arrow 478 pointing towards theleft, a profile graph is illustrated from which a position in theselector track can be recognized.

The continuation of the time graphs 470, 472, 474, 476, 477 to the rightof the broken line 480 will serve to explain through an example howpositions and states of the shifter finger can be detected on the basisof the time profiles of the illustrated variables.

The method is performed under voltage control. This means that asubstantially constant voltage is used to energize the shifter andselector motor, so that the voltage signals 470, 472 have constantvalues. It should be noted at this point, that the scope of theinvention nevertheless also includes a control that works with variablevoltages.

The start of the shifter and selector motors causes a current surge inthe control device at the point 482. At this point in time, the shifterfinger is constrained in a shift track, so that it can only move in theshift direction as can be seen in the area 484 of the displacementgraph.

After the start-up phase of the motors, the current in the controldevice decreases and continues at an essentially constant level duringthe phase 486. As the shifter finger is constrained by the shift trackfrom moving transverse to the latter, it can only advance in the shiftdirection, as indicated by the increasing displacement in the bottomgraph of FIG. 10. At the position 488 in the displacement graph, theshifter finger has essentially reached the selector track. Due to theactuation force of the selector motor, the shifter finger from thispoint on can also move in the selector direction, as indicated by theportion 490 of the displacement graph.

As the shifter finger is no longer constrained by the shift track andbegins to move in the selector direction, the total current of thecontrol device decreases and settles at an essentially constant level inthe area 492.

By detecting the foregoing development in the current profile, it ispossible to determine that the movable element has reached the selectortrack.

The continuation of the graphs in FIG. 10 to the right of the brokenline 480 represents two cases (a) and (b) which can occur alternatively.If at the time 494, the shifter finger runs into a stop in the selectordirection while the selector motor continues to receive a voltage asshown by the graph 472, the total current increases as shown at 496 andthen settles at a higher, essentially constant level 498. The shifterfinger continues to move in the shift direction, as shown in the portion500 of the displacement graph. If at the time 502, the shifter fingerruns into a stop in the shift direction, the current increases again inthe area 504 and then settles again at a higher, essentially constantlevel 506.

If the shifter finger at the time 494 is blocked both in the shift andselector direction, the total current of the control device will rise toa higher level in the area 508, essentially equal to the current level506. Thus, a higher current level that reflects blockage in bothdirections can be detected already between the times 494 and 502 andinterpreted as a position where the movable element is constrained fromfurther movement by stops in both directions.

FIG. 11 shows as an example in flow-chart format how limitations in thelengthwise direction of the selector track can be detected.

In step 520, the selector motor is energized with current, so that theshifter finger moves in the lengthwise direction of the selector track.

In step 522, a rise in the total current of the control device isdetected, indicating that the shifter finger has reached a stop at theend to the selector track.

In step 524, the selector motor is switched off.

FIG. 12 shows as an example in flow-chart format how the inventivemethod can be used under an emergency procedure to put the transmissioninto predetermined gears, such as first, second and reverse gear.

In step 530, a voltage is applied to the shifter motor to move theshifter finger along a shift track.

In step 532, a rise in the current of the control device is detected,which is followed by the detection of a decrease in current in step 534.This indicates that the shifter finger has run into a kind of temporarybarrier in the shift direction. This happens when a synchronizationpoint is reached, which temporarily blocks the shifting movement andcauses the current to rise. After the rpm rates are synchronized, theblockage is released so that the shifter finger can continue itsmovement in the shift direction, which causes the current to decreaseagain.

In step 536, the current is found to increase again and to remain at theincreased level for at least a predetermined length of time. This can beinterpreted as an indication that the shifter finger has reached thedead end of the shift track. The shifter motor is switched off at thispoint. Subsequently, voltage pulses of alternating polarity are appliedto the shifter motor in order to cause the shift mechanism to settle ina bias-free position.

In step 538, the shifter motor is switched off, after a predeterminedtime period has elapsed, for example 200 to 1000 milliseconds. Delayingthe switch-off point by a predetermined amount serves to ensure that theshifter finger is not at a synchronization point.

FIG. 13 represents a schematic view of portions of a transmissionaccording to the invention.

The components of the transmission that are shown include in particulara control device 550, a selector motor 552, a shifter shaft 554, ashifter finger 556, and a shifting rod 558. A shifter motor is not shownin this example.

An incremental sensor device for the displacement in the selectordirection is arranged at the selector motor (not shown).

An additional incremental displacement sensor 560 is arranged as aredundant means of detecting displacement in the selector direction.

The redundant incremental displacement sensor 560 as well as theselector motor 552 have signal connections to the control device 550, assymbolized by the lines 562 and 564.

The redundant incremental displacement sensor 560 uses a non-contactingprinciple to sense a surface profile of the shifter shaft 554 as thelatter moves along the sensor. The sensor 560 is based, e.g., on theHall-effect sensor principle or an inductive sensor principle.

Each of the FIGS. 14 and 15 shows a selecting/shifting trackarrangement.

The graphs 570 and 572 below the representations of theselecting/shifting track arrangements represent sensor signals of thekind that could be produced by the redundant incremental displacementsensor of FIG. 13. As shown in FIG. 14, the sensor or switch 560 couldgive a signal when the shifter finger has reached one of the positionswhere the shift tracks branch off from the selector track.

Alternatively, the sensor 560 could also be designed to give a signalonly when the shifter finger is at one specific position within theselector track, e.g., the middle shift track in a double-H arrangement.

With preference, the redundant incremental displacement sensor 560 forthe selector direction has a coarser measuring resolution than theprimary incremental sensor device that is arranged, e.g., at theselector motor.

The arrangement of FIG. 16 differs from FIG. 13 essentially in theredundant incremental displacement sensor which in the case of FIG. 16is configured as a mechanical, spring-biased contact feeler element thatfollows a contour profile of the shifter shaft 554.

The block diagram 1700 of FIG. 17 represents a schematic model of anactuator device. A target value is generated in the electric controldevice 1701 of the transmission and sent to a position regulator 1702which, as a result, generates a corresponding voltage U_(A). The voltageU_(A) is transmitted by way of an output stage 1703 and serves tocontrol an actuator device such as a rotary electric motor 1704. Theactuator device 1704 moves the actual shifter elements of thetransmission 1705 by way of a motion-transfer mechanism (not shown). Inthe case of a shift transmission that works in discrete steps throughdifferent gear pairs, the shifter elements are the sliding sleeves thatengage and disengage the free gears. An incremental displacement sensor1706 generates a signal indicating the position or a change in theposition of a movable element in relation to a reference point. Inanother embodiment, it may also be advantageous to use other kinds ofdisplacement sensors including, e.g., absolute displacement sensors suchas potentiometers. The signal generated by the displacement sensor 1706is fed back to blocks 1701 and 1702 and at the same time transmitted toan error-detection unit 1707. The voltage U_(A)generated in block 1702is further entered into an emulator unit 1708, i.e., a computer model ofan actuator device that is implemented in an electrical control device.

The portion of FIG. 17 that is framed by a broken line illustrates thedetails of the block 1708, i.e., an emulation of a drive source for anactuator, in this case a rotary electric DC motor. The model uses anappropriate transfer function to generate a signal that is equivalent tothe displacement signal generated by the incremental displacement sensor1706 as a result of a voltage signal U_(A) coming out of block 1702. Thetransfer function of the emulator model 1708 is based on the followingset of equations:

U _(A) =R _(A) ·I _(A) +C _(M)·ω_(M)  (1)

M _(A) =C _(M) ·I _(A)  (2)

J _(M)·{dot over (ω)}_(M) =M _(A) −d·ω _(M)  (3)

$\begin{matrix}{ \Rightarrow{\overset{.}{\omega}}_{M}  = {{\frac{c_{M}}{R_{A} \cdot J_{M}} \cdot U_{A}} - {( {\frac{c_{M}^{2}}{R_{A} \cdot J_{M}} + \frac{d}{J_{M}}} ) \cdot \omega_{M}}}} & (4)\end{matrix}$

The symbols used in the foregoing equations will be defined in thenext-following paragraph below. The transfer function corresponding toequations (1) to (4) describes a servo-loop of a type known as IT₁(integrating control loop with a time lag). To represent the entirecontrol loop consisting of the control device and the actuator device, atransfer behavior known as PT₂ (proportional control with a second-ordertime lag) will be entirely adequate. An alternative embodiment isconceivable where the emulator model would be used alone without theincremental position sensor to determine a change in position an/or theposition itself in relation to a reference point. In this latter case,it is advantageous to use a more advanced model of the actuator drivemechanism.

The emulator model 1708 in FIG. 17 is represented in detail by thefunctional blocks 1709 to 1716. In block 1709, the input quantity U_(A)is multiplied by the reciprocal value 1/R_(A) of the rotor resistanceR_(A) of the actuator motor. After block 1710, the feedback from block1714 is subtracted. Block 1710 performs a division by the moment ofinertia J_(M) of the rotor of the actuator motor. After block 1710, thefeedback from block 1713 is subtracted. In block 1712, an integration isperformed to calculate the angular velocity ω_(M) of the actuator motor.In block 1714, the result of block 1712 is multiplied by thevelocity-dependent friction constant d of the actuator drive and fedback to the output of block 1709. In block 1713, the result of block1712 is multiplied by the quotient C_(M)/R_(A) and fed back to theoutput of block 1710. A further integration of the angular velocityω_(M) in block 1715 produces the angular position φ_(M). In block 1716,the angular position φ_(M) (e.g. in radian units) is converted to aquantity that corresponds to the increments measured by the incrementalposition sensor.

FIG. 18 shows an example of an error-detection strategy in block-diagramformat. Block 1801 of the block diagram 1800 stands for a positioncontroller generating a control signal and sending it simultaneouslyalong two different paths. From the left-hand output of block 1801, thecontrol signal is fed through an end stage (block 1802) to a drive motor(block 1803) causing a position change which, in turn, is detected by adisplacement sensor (block 1804) such as an incremental position sensor.From the right-hand output of block 1801, the same control signal issent to an emulator model of the drive motor (block 1805) which computesa signal that is the theoretical counterpart of the actually detectedsignal of block 1804. In block 1806, the difference between the actualand the theoretical signal is determined. Block 1807 performs acomparison whether or not the difference is larger than a giventhreshold value. In the affirmative case of block 1807, an entry is madeinto an error memory (block 1808), and an error-managing strategy isinitiated in block 1809. In the negative case of block 1807, thedisplacement-sensor signal is accepted as correct. In block 1810, theemulator model (block 1805) is adjusted so that the computed signalsvalues of the emulator model (block 1805) will more closely match theactual signal values of the displacement sensor (1804).

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic and specific aspects of theaforedescribed contribution to the art and, therefore, such adaptationsshould and are intended to be comprehended within the meaning and rangeof equivalence of the appended claims.

What is claimed is:
 1. A method of detecting a change in positionrelative to a reference point of a transmission that is shiftable into aplurality of shift positions corresponding to different rotary transferratios between an input shaft and an output shaft, wherein changes fromone shift position to another are associated with movements of a firstshifter element in a two-dimensional shift pattern comprising a selectortrack and shift tracks, a first electrical actuator actuates movementsalong the selector track, and a second electrical actuator actuatesmovements along the shift tracks, at least one of the actuatorscomprises a displacement-sensor device, and the transmission comprisesan electrical control device to control the actuators; the methodcomprising the step of emulating at least one of the actuators by meansof a model in the electrical control device, wherein the model serves todetect a malfunction of the displacement-sensor device, wherein themodel produces an emulator output signal, the at least one actuatorproduces an actuator output signal, and the malfunction is detected byfinding a difference between said output signals.
 2. The method of claim1, wherein the actuator emulation is performed by means of acontrol-loop emulator.
 3. The method of claim 2, wherein the at leastone actuator and the control-loop emulator are given equivalent inputsignals.
 4. The method of claim 3, wherein a voltage is used as inputsignal for the control-loop emulator.
 5. The method of claim 4, whereinthe voltage comprises the input voltage of a position controller.
 6. Themethod of claim 2, wherein the control-loop emulator generates anemulator output signal that is equivalent to a displacement-sensoroutput signal.
 7. The method of claim 6, wherein the emulator outputsignal comprises one of an angular position and a quantity from which anangular position can be calculated.
 8. The method of claim 7, whereinthe emulator output signal corresponds to a magnitude of an angleexpressed as a number of increments.
 9. The method of claim 7, whereinthe emulator output signal corresponds to a magnitude of an angleexpressed in radian units.
 10. The method of claim 2, wherein thecontrol-loop emulator uses characteristic variables of the actuatordevice that is being emulated.
 11. The method of claim 10, wherein thecharacteristic variables comprise at least one of an rpm rate and arotary acceleration of the actuator device that is being emulated. 12.The method of claim 2, wherein the control-loop emulator usescharacteristic design parameters of the actuator device that is beingemulated.
 13. The method of claim 12, wherein actuator device comprisesan electric motor with a rotor and a stator and the characteristicdesign parameters comprise at least one of a moment of inertia, anelectrical resistance, and a torque constant of the rotor.
 14. Themethod of claim 2, wherein the control-loop emulator uses at least onemeasured quantity of the actuator device that is being emulated.
 15. Themethod of claim 14, wherein the measured quantity consists of aspeed-dependent amount of friction.
 16. The method of claim 1, whereinan error-managing strategy is initiated after detecting the malfunction.17. The method of claim 16, wherein in addition an entry is made into anerror memory.
 18. A method of detecting a change in position relative toa reference point of a transmission that is shiftable into a pluralityof shift positions corresponding to different rotary transfer ratiosbetween an input shaft and an output shaft, wherein changes from oneshift position to another are associated with movements of a firstshifter element in a two-dimensional shift pattern comprising a selectortrack and shift tracks, a first electrical actuator actuates movementsalone the selector track, and a second electrical actuator actuatesmovements along the shift tracks, at least one of the actuatorscomprises a displacement-sensor device, and the transmission comprisesan electrical control device to control the actuators; the methodcomprising the step of emulating at least one of the actuators by meansof a model in the electrical control device, wherein the actuatoremulation is performed by means of a control-loop emulator, wherein thecontrol-loop emulator generates an emulator output signal that isequivalent to a displacement-sensor output signal, wherein the emulatoroutput signal is used as a substitute for the displacement-sensor outputsignal to control the actuator that is being emulated.
 19. A method ofdetecting a change in position relative to a reference point of atransmission that is shiftable into a plurality of shift positionscorresponding to different rotary transfer ratios between an input shaftand an output shaft, wherein changes from one shift position to anotherare associated with movements of a first shifter element in atwo-dimensional shift pattern comprising a selector track and shifttracks, a first electrical actuator actuates movements along theselector track, and a second electrical actuator actuates movementsalong the shift tracks, at least one of the actuators comprises adisplacement-sensor device, and the transmission comprises an electricalcontrol device to control the actuators; the method comprising the stepof emulating at least one of the actuators by means of a model in theelectrical control device, wherein at a time when the displacementsensor device is fully functional, if a discrepancy is detected betweenthe emulator output signal and the displacement-sensor output signal, anadjustment is made to reduce said discrepancy.
 20. The method of claim19, wherein said adjustment consists of adapting the model so that theemulator output signal will more closely match the displacement-sensoroutput signal.
 21. A control device for a vehicle transmission, saidtransmission comprising: a shift pattern with a selector track and shifttracks; a first shifter element, movable in the shift pattern; a secondshifter element; a first electrically controlled actuator device foractuating for actuating movements along the selector track, and a secondelectrically controlled actuator device for actuating movements alongthe shift tracks; a position-sensor device for detecting a currentposition of at least one of said shifter elements; wherein the controldevice comprises an emulator model of at least one of the actuatordevices, wherein the model serves to detect a malfunction of theposition-sensor device and the model produces an emulator output signal,the at least one actuator produces an actuator output signal, and themalfunction is detected by finding a difference between said outputsignals.
 22. A control device for a vehicle transmission, saidtransmission is shiftable into a plurality of shift positionscorresponding to different rotary transfer ratios between an input shaftand an output shaft, comprising: a two-dimensional shift pattern with aselector track and shift tracks; wherein changes from one shift positionto another are associated with movements of a first shifter element inthe shift pattern, a the first shifter element, being movable in theshift pattern; a second shifter element; a first electrical actuatoractuates movements along the selector track, and a second electricalactuator actuates movements along the shift tracks, at least one theactuators comprises a displacement-sensor device, wherein the controldevice comprises an emulator model of at least one of the actuatordevices, wherein at a time when the displacement sensor device is fullyfunctional, if a discrepancy is detected between the emulator outputsignal and the displacement-sensor output signal, an adjustment is madeto reduce the discrepancy.